Dynamic soil–structure interaction of monopile supported wind turbines in cohesive soil.

Offshore wind turbines supported on monopile foundations are dynamically sensitive because the overall natural frequencies of these structures are close to the different forcing frequencies imposed upon them. The structures are designed for an intended life of 25 to 30 years, but little is known about their long term behaviour. To study their long term behaviour, a series of laboratory tests were conducted in which a scaled model wind turbine supported on a monopile in kaolin clay was subjected to between 32,000 and 172,000 cycles of horizontal loading and the changes in natural frequency and damping of the model were monitored. The experimental results are presented using a non-dimensional framework based on an interpretation of the governing mechanics. The change in natural frequency was found to be strongly dependent on the shear strain level in the soil next to the pile. Practical guidance for choosing the diameter of monopile is suggested based on element test results using the concept of volumetric threshold shear strain.

Monitoring of a novel FlexiArchTM bridge system to investigate soil-structure interaction

Masonry arch bridges are one of the oldest forms of bridge construction and have been around for thousands of years. Brick and stone arch bridges have proven to be highly durable as most of them have remained serviceable after hundreds of years. In contrast, many bridges built of modern materials have required extensive repair and strengthening after being in service for a relatively short part of their design life. This paper describes the structural monitoring of a novel flexible concrete arch known as: FlexiArchTM. This is a bridge system that can be transported as a flat-pack system to form an arch in-situ by the use of a flexible polymeric membrane. The system has been developed under a Knowledge Transfer Partnership between Queen’s University Belfast (QUB) and Macrete Ltd. Tievenameena Bridge in Northern Ireland was a replacement bridge for the Northern Ireland Roads Service and was monitored under different axle loadings using a range of sensors including discrete fiber optic Bragg gratings to measure the change in strain in the arch ring under live loading. This paper discusses the results of a laboratory model study carried out at QUB. A scaled arch system was loaded with a simulated moving axle. Various techniques were used to monitor the arch under the moving axle load with particular emphasis on the interaction of the arch ring and engineered backfill.

Avaliação do efeito da interação solo estrutura sobre o comportamento estrutural de edificações em aço e mistas (aço concreto).

O conhecimento do tema da interação solo-estrutura permite que as edificações sejam projetadas de maneira mais realista com o comportamento físico. Há décadas atrás seria inviável um dimensionamento considerando a deformabilidade do solo de fundação, e as estruturas eram dimensionadas adotando-se as fundações como indeslocáveis, sob uma base rígida. Essa consideração conduz a respostas estruturais inadequadas, por vezes comprometendo a segurança e a estabilidade do conjunto estrutural. Atualmente, o avanço tecnológico permite a obtenção de resultados de milhões de cálculos matemáticos em questões de segundos, podendo-se obter soluções mais arrojadas e dinâmicas, facilitando o dimensionamento estrutural de forma a atender ao novo padrão de construção e arquitetura. A relevância de tal assunto motivou a análise numérica de um edifício de 4 pavimentos de estrutura mista (aço-concreto), considerando o efeito da interação solo-estrutura. As análises foram conduzidas com o programa ANSYS, de elementos finitos, substituindo-se os apoios indeslocáveis por molas discretas, lineares e elásticas, com rigidez equivalente ao solo, conforme hipótese de Winkler. Os parâmetros dos solos de fundação foram adquiridos a partir de correlações empíricas existentes na literatura e da utilização do programa computacional PLAXIS para a determinação das constantes elásticas das molas. Neste trabalho, foram comparados os resultados de reações verticais, esforços normais, momentos fletores e deslocamentos da estrutura obtidos pelo modelo clássico de projeto, que considera apoios indeslocáveis, e pelo modelo de Winkler, que considera a interação solo-estrutura. As análises foram executadas para seis diferentes tipos de solos argilosos, siltosos e arenosos. Os resultados obtidos mostraram claramente a redistribuição dos momentos fletores, esforços normais e reações verticais nos pilares com diferenças significativas para os pilares de canto e periféricos. Observou-se uma tendência de alívio dos esforços nos pilares mais solicitados, adotando a estrutura assentada em uma base rígida. As análises ressaltaram a relevância da interação solo-estrutura, com efeitos provenientes do rearranjo do solo de fundação nos elementos estruturais das edificações.

Development of a new apparatus for modeling deep excavation related problems in geotechnical centrifuge

Underground space is commonly exploited both to maximise the utility of costly land in urban development and to reduce the vertical load acting on the ground. Deep excavations are carried out to construct various types of underground infrastructure such as deep basements, subways and service tunnels. Although the soil response to excavation is known in principle, designers lack practical calculation methods for predicting both short- and long-term ground movements. As the understanding of how soil behaves around an excavation in both the short and long term is insufficient and usually empirical, the judgements used in design are also empirical and serious accidents are common. To gain a better understanding of the mechanisms involved in soil excavation, a new apparatus for the centrifuge model testing of deep excavations in soft clay has been developed. This apparatus simulates the field construction sequence of a multi-propped retaining wall during centrifuge flight. A comparison is given between the new technique and the previously used method of draining heavy fluid to simulate excavation in a centrifuge model. The new system has the benefit of giving the correct initial ground conditions before excavation and the proper earth pressure distribution on the retaining structures during excavation, whereas heavy fluid only gives an earth pressure coefficient of unity and is unable to capture any changes in the earth pressure coefficient of soil inside the zone of excavation, for example owing to wall movements. Settlements of the ground surface, changes in pore water pressure, variations in earth pressure, prop forces and bending moments in the retaining wall are all monitored during excavation. Furthermore, digital images taken of a cross-section during the test are analysed using particle image velocimetry to illustrate ground deformation and soil–structure interaction mechanisms. The significance of these observations is discussed.

Experimental and numerical investigation of the seismic behavior of rectangular tunnels in soft soils

Underground structures constitute crucial components of the transportation networks. Considering their significance for modern societies, their proper seismic design is of great importance. However, this design may become very tricky, accounting of the lack of knowledge regarding their seismic behavior. Several issues that are significantly affecting this behavior (i.e. earth pressures on the structure, seismic shear stresses around the structure, complex deformation modes for rectangular structures during shaking etc.) are still open. The problem is wider for the non-circular (i.e. rectangular) structures, were the soilstructure interaction effects are expected to be maximized. The paper presents representative experimental results from a test case of a series of dynamic centrifuge tests that were performed on rectangular tunnels embedded in dry sand. The tests were carried out at the centrifuge facility of the University of Cambridge, within the Transnational Task of the SERIES EU research program. The presented test case is also numerically simulated and studied. Preliminary full dynamic time history analyses of the coupled soil-tunnel system are performed, using ABAQUS. Soil non-linearity and soil-structure interaction are modeled, following relevant specifications for underground structures and tunnels. Numerical predictions are compared to experimental results and discussed. Based on this comprehensive experimental and numerical study, the seismic behavior of rectangular embedded structures is better understood and modeled, consisting an important step in the development of appropriate specifications for the seismic design of rectangular shallow tunnels.

Pontes integrais: estado da arte

Dissertação para obtenção do grau de mestre em Engenharia Civil

Springboards into design : exploring multiple representations of interaction in a dental surgery

This paper demonstrates that in order to understand and design for interactions in complex work environments, a variety of representational artefacts must be developed and employed. A study was undertaken to explore the design of better interaction technologies to support patient record keeping in a dental surgery. The domain chosen is a challenging real context that exhibits problems that could potentially be solved by ubiquitous computing and multi-modal interaction technologies. Both transient and durable representations were used to develop design understandings. We describe the representations, the kinds of insights developed from the representations and the way that the multiple representations interact and carry forward in the design process.

Interactive lounge : an interdisciplinary approach to the design of a gestural interaction device

Among the many new opportunities that digital technologies are enabling are an increased capacity for viewers to interact not only with the program content, but with an increasingly wide array of other digital applications. Within this context this project has developed a new interaction device (incorporating gestural platform technology) and user interfaces to facilitate interactive access to digital media in a lounge room setting. This paper provides an overview of an interdisciplinary design process applied by Australasian CRC for Interaction Design (ACID) researchers—in order to develop the device and present in detail its unique features.

Co-constructed interaction in a paired speaking test : the rater's perspective

The definition and operationalisation of interactional competence in speaking tests that entail co-construction of discourse is an area of language testing requiring further research. This article explores the reactions of four trained raters to paired candidates who oriented to asymmetric patterns of interaction in a discussion task. Through an analysis of candidate discourse combined with rater notes, stimulated verbal recalls, rater discussions and scores awarded for interactional effectiveness, the article examines the extent to which raters compensate or penalise candidates for their role in co-constructing asymmetric interactional patterns. The article argues that key features of the interaction are perceived by the raters as mutual achievements, and it further suggests that the awarding of shared scores for interactional competence is one way of acknowledging the inherently co-constructed nature of interaction in a paired speaking test.

Childhood and social interaction in everyday life : an epilogue

The epilogue pulls together the conceptual and methodological significance of the papers in the special issue exploring childhood and social interaction in everyday life in Sweden, Norway, United States and Australia. In considering the special issue, four domains of childhood are identified and discussed: childhood is a social construct where children learn how to enter into and participate in their social organizations, competency is best understood when communicative practices are examined in situ, children’s talk and interaction show situated culture in action, and childhood consists of shared social orders between children and adults. Emerging analytic interests are proposed, including investigating how children understand locations and place. Finally, the epilogue highlights the core focus of this special issue, which is showing children’s own methods for making sense of their everyday contexts using the interactional and cultural resources they have to hand.